High-stability glycol alginates and their manufacture



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ATTORNEY Jan. 17, 195o HIGH-STABILITY GLYCOL ALGINATES AND THEIR MANUFACTURE Arnold B. Steiner, La Jolla, and William H. Mc-

Neely,- San Diego, Calif., assignors to Kelco Company, San Diego, Calif., a corporation of Delaware Application December 22, 1945, Serial No. 636,938

20 Claims. (Cl. 26o-209.6)

This invention relates to reactions between alginic acid and the epoxy-paraiiins or alkylene oxides by which the properties of the acid are changed in a. manner which imparts a new utility to the product.

More specifically, the invention relates to improvements in a heretofore disclosed method of manufacturing glycol alginates by which the properties of the product are materially bettered while the manufacturing cost is reduced.

In a copending application filed April 3, 1944, byArnold B. Steiner under Serial No. 529,423, now Patent No. 2,426,125, it is disclosed that alginic acid may be reacted directly with the alkylene oxides to form a hitherto unknown series of addition compounds which have been termed glycol alginatesl These compounds differ in properties from alginic acid and the alkali metal alginates in the following respects.

Alginic acid is substantially insoluble in water; its salts with the alkali metals. magnesium, ammonium and many organic bases are freely water-soluble, forming colloidal solutions of high viscosity. The glycol alginates are freely watersoluble and form viscous and colloidal aqueous solutions.

Alginic acid combines readily with basic substances such as the soluble hydroxides and carbonates but reacts slowly if at all with any of the neutral metallic salts; the soluble alginates (limiting that term to the salts described in the paragraph above) form gels or gelatinous precipitates with water-soluble salts of the alkalineearth metals (except magnesium), and of aluminum and the heavy metals. By contrast, the glycol alginates show much less reactivity with the salts which precipitate the soluble alginates.

Alginic acid is a rather strong acid (p1-1 1.8 to 2.5 in 1% aqueous dispersion); its water-soluble salts 'are decomposed with precipitation of the substantially insoluble acid in mediabelow about pH 4. The glycol alginates,'when made by the method of the copending application, are strongly acidic, usually pH 3 or even lower. the method herein disclosed the hydrogen ion concentration may be controlled vup to about pH 5. In neither case are solutions of the glycol alginates precipitated or gelatinzed by even the strongv acids.

The varied utilities of the three products follow from this difference in properties. Alginic acid per se has little usefulness other than as the raw material from which its salts are made. The soluble salts have a high degree of utility in situations in which gelatinization is desired, but where gel formation is to be Iavoided they cannot be used in any acid medium and can be made compatible with calcium-containing liquids such as milk only by an elaborate formulation with buffers or with precipitants for calcium ions. The glycol alginates may be used freely in acid media and somewhat less freely in milk and may be protected against gelatinization when mixed with liquids richer in calcium by control of the concentration of the alginate and of the pH value of the medium.

The method described in the copending application is very simple. The moist alginic acid is treated, in a subdivided state, with an alkylene oxide at a temperature usually ranging from C. to 77 C. in a closed vessel, the reaction usually being completed in from one to three hours. The product occurs in the brous state (unless a large excess of water be present) and in its original degree of comminution. No further preparation is required than to evaporate any excess oxide which it may contain and to bring lthe water content to a standard.l

While the method described in the copending application is fully functional, we have further discovered that some of the properties of the product may be improved, and the quantity of oxide required for the reaction may be reduced, by making use of certain manipulative steps not covered in the copending application, and which are the subject matter of the instant disclosure.

PARTIAL NEUTRALIZATION The discovery on which the new manipulation is grounded is of the utility of a partial neutralization of the alginic acid prior to the reaction with an alkylene oxide. The'application of this step renders it possible to stabilize the product by raising its pH value above the critical level and to reduce the number of free carboxyl groups present in the nal product. It also facilitates the production of a fully soluble alginate, reduces the extent to which both the alginic acid and the 3 alkylene oxide are hydrolized during the esterifying reaction, and materially accelerates the reaction between the oxide and the acid.

It would be reasonable to anticipate that the partial neutralization of alginic acid with a basic substance, followed by esterication of the free acid remaining, would produce a mixture of a glycol alginate with a water-soluble alginic salt, and that solutions of such a mixture would be gelatinized by acids. This anticipated result did not occur, the product of esterication of the partially neutralized acid being compatible with acids in all strengths.

Further, while alginic acid is substantially insoluble, the product of partial esteriflcation of the free acid remaining after partial neutralization is fully soluble, even when thirty percent or over of the original acidity remains unsatisfied.

It is believed, therefore, that when a quantity of a base insufcient for complete neutralization is added to the acid it does not completely neutralize a portion of the molecules of acid, leaving the remaining molecules wholly uncombined but, rather, that it distributes itself in such manner as' to satisfy a portion only of the carboxyl groups of each molecule. For the same reason it seems probable that the remaining carboxyl groups of each molecule may be completely or partially blocked by esteriiication, in the manner illustrated in the structural formulae shown in the attached drawing.

In these diagrams, which offer the most probable explanation of the peculiar behavior of a partially neutralized and partially esteritled product: Fig. 1 shows the known structure of alginic acid; Fig. 2 shows the known result of complete neutralization of the carboxyl groups with, for example, sodium; Fig. 3shows the probable structure of the product resulting from complete esterication with, for example, ethylene oxide, and Fig. 4 illustrates the probable structure of the product resulting from partial neutralization followed by incomplete esteriiication of the remaining carboxyl groups.

Alginic acid is known to consist in great part of anhydro-D-mannuronic acid residues linked glycosidically in accordance with the formula of Fig. l. In this structure the mannuronic units are linked in such manner that the carboxyl groups are free to react while the aldehyde lgroups are shielded by linkages. It will be understood that this and the succeeding diagrams represent only three links in a very long polymeric chain, the molecular weights indicating that a high-viscosity acid may have from one hundred to several hundred mannuronic units in the chain.

The theoretical combining weight of alginic acid is the weight of one mannuronic unit (176) regardless of the number of units in the polymer. The actual combining weight of the commercial acldis nearer 215, indicating the presence of unknown, nontitratable substances. When alginic acid is combined with sodium in the proportion (about) 215:23 the productis a neutral salt, the structure being as in Fig. 2 which shows all the carboxyl groups satisfied by the base.

If it were possible Wholly to esterify alginic acid, the structure of the product would be as illustrated in Fig. 3, in which the replaceable hydrogen of each carboxyl has attached to the oxygen of the oxide and through it to one of the carbons while the other carbon links with the terminal oxygen of the carboxyl. The validity of this structure is supported by the observation that alkalis decompose the ester, forming the salt of Fig. 2.

In Fig. 4 the carboxyl of the rst unit in the fragmental chain has been satisfied with sodium, that of the second with ethylene oxide while the third carboxyl remains unrcted. In a chain having a hundred or more umts each having one carboxyl group, both neutralization and esteriflcation may proceed by very small increments and the resultant product may have any percentage proportion of its carboxyl groups combined with the base, or with the oxide, or free, according to the extent to which each reaction is carried.

It is recognized also that some of the carboxyl groups of the alginic acid may be esteriiied with the hydroxy groups of the alginic acid. Thus the reaction may occur (1) Between the carboxyl group and the hydroxyl group of the same anhydro-D-mannuronic residue, as illustrated in Fig. 5;

(2) Between the carboxyl group of one anhydro-D-mannuronic residue and the hydroxyl* group of another such residue in the same molecule, as illustrated in Fig. 6;

(3) Between the carboxyl group of an anhydro- D-mannuronic acid residue in one molecule and the hydroxyl group of another such residue in another molecule, as illustrated in Fig. 7.

STABILITY or' PaonUc'r Products made by the method described in the copending application, in which alginic acid is reacted with an alkylene oxide without any modiilcation of the acidity of the acid, proved in some instances to be lacking in stability, tending to change (usually to depreciate) in viscosity during storage in the solid condition.

It was discovered that this instability is due to too great acidity of the product and investigation disclosed that'the critical level is in the range pH 3.5 to pH 3.9. At the latter iigure no change whatever was observed after three months storage; at pH 3.5 the change taking place in that period was of no importance; at pH 3.0, which is about as high as can be had in the terication of an unmodied acid (pH 1.8 to pH 2.0), a. material change in the viscosity of a solution of given strength often occurred in a shorter time, accompanied by decreasing solubility and, occasionally, by a tendency toward gelatinization of the solution.

The low pH product obtained by esterification of an unmodified acid cannot be brought to a higher pH by the addition of alkalis to the iinished product, by reason of the splitting of the ester on contact with the base.

f This dimculty is avoided by neutralizing, in advance of the alkylene oxide reaction, a small proportion, usually from 5% tol 20% but sometimes up to 30%, of the carboxyl groups of the alginic acid to be reacted. It was anticipated that this step might interfere with the esterifying reaction, but on the contrary the undesired hydrolysis of the oxide to the corresponding glycol was strongly restrained, the desired glycol alginate reaction was accelerated, and the consumption of alkylene oxide was materially reduced.

SELECTION or a Bass The base used to eilect this partial neutralization may be any base producing a water-soluble salt with alginic acid, to wit: ammonia or the lower amines or any of the basic compounds of the alkali metals or of magnesium. As the acid is magari a water-insoluble compound, ammonia or the volatile amines are preferred as being the most readilly dispersed. In instances where the presence of an ammonium salt in the finished product may be objectionable, sodium, potassium or the more costly alkali metals are equally eil'ective.

The preferred base may be used in the form of the hydroxide, the carbonate or a phosphate. The substantial equivalence oi three of these bases, which may be considered as typifying hydroxides. carbonates and phosphates, is indicated in the following comparison in which samples of the same batch oi alginic acid were partially neutralized with different bases and then esteriiied with equal ratios of alkylene oxide to acid under identical conditions.

Mnrnons or Nsu'rnlinc The method of application of the neutralizing agent should be such as to approach the ideal condition in which a part of the carboxyl groups of each polymeric chain of the acid are combined, rather than all the carboxyls of part of the acid. Because of the substantial insolubility of the acid and the necessity for treating it with the base while in solid form, the tendency is for the basic substance to act only on the outer surfaces of the acid particles, producing a condition which is unfavorable to the subsequent esteriflcation reaction.

To overcome this tendency so far as may be we first bring the acidto the physical condition in which it is most amenable to reaction with the base. This involves reduction of the water content of the acid which, as it comes from the manufacturing process is of the order of 80% or more, to approximately 50% by weight. A desirable way of producing this reduction is by repeated passage of the acid through a hammer mill supplied with a current of warm, dry air but any method of drying by gentle heating, evacuation or extraction with alcohols may be used. A water content ranging from 45% to 55%, while not critical, has been found to give the best reaction rate for the esterification with the least hydrolysis of the alkylene oxide. The reduced water content strongly facilitates subdivision, the product of this combined drying and shredding step being a fluffy mass of fine, thread-like fibres which expose a very large surface area per unit of mass.

Partial neutralization with ammonia may be produced either during or after the completion of the drying step. In the first alternative, gaseous ammonia is introduced into the air current used for drying. In the second, the fluffed and dried acid is placed in an autoclave, which may desirably be flushed out with gaseous ammonia to remove air. The ammonia, in aqueous solution or in gaseous form, is then introduced and the mass stirred for perhaps an hour, preferably under superatmospheric pressure and at a dil temperature above atmospheric, as for exple 35 cent.

For neutralization with a carbonate of an alkali metal or of ammonia a somewhat diderent procedure is advisable. The acid is first roughly subdivided by three or four passes through the hammer mill, without drying. A small amount of a wetting agent, as for example a 10% solution of the dioctyl ester of sodium sulfosuccinic acid, known commercially as Aerosol OT, is then added and followed by a. milky slurry oi a dilute aqueous solution of the carbonate dispersed in an equal volume of a low boiling-point alcohol or ketone. After an additional few minutes of stirring the mixture of acid and base is withdrawn from the mixing vessel and dried and flufled as above described, by repeated passes through a hammer mill. The greater part of the subdivision of the acid particles occurs after the addition of the base and thus the base is thoroughly disseminated through and reacted with the acid during the drying and comminuting step.

For neutralizing with an alkali metal phosphate such as trisodium phosphate, it is preferable to add to the undried acid about one-half its weight of an alcohol such 'as isopropanol. rllhe mixture is stirred for a few minutes, after which the suspension of the nely ground phosphate in a further small quantity af alcohol is added, the mixture being stirred for some time to cause the particles of the salt to become attached to the acid fibres. The liquid is then drained off and the mass pressed to expel as much liquid as possible, after which it is iluffed as above described. The water content is adjusted during this step, by heating or by addition of water.

The alkali metal phosphate can also be added in the form of an aqueous solution or of a powder to the alginic acid during the iiuiiing step prior to drying or to the acid which has been dried to about 50% solids.

Erracrs or PARTIAL NEU'rRALIzA'rIon The edectiveness of the above described step of partial neutralization in increasing esteriflcation and in raising the pH value of the product is illustrated in the following comparison. To obtain these iigures identical samples of alginic acid were treated with ammonia to various degrees of partial neutralization and were then reacted with equal quantities of an alkylene oxide under identical conditions.

Table 2 Percent Carboxyl Groups Base Used Pgnlct Neutralizcd Esteried Total 0. 0 70. 0 3. 0 5.0 67 72.() 3. I 10.0 76 86.0 3. 5 l2. 5 80 92. 5 3. 8 15.0 82 97.0 4. i 30. 0 69 99. 0 4. 7

f pH in 1%Vaqucous solution.

Erracrs or TEMPERATURE VAruATIoNs The differences in result produced when an unmodified acid is treated with an alkylene oxide for equal periods at different temperatures is' illustrated in the following table. In these treatments the method was identical in each case except as noted in the table.

These and other experiments indicate that at a temperature as low as 35 C. the reaction between acid and oxide proceeds so slowly that the reaction time of about eight hours is suiiicient for thesubstantially complete 'utilization of the alkylene oxide at 50 C. In the twenty-two hour oxide is incompletely utilized, an excessive pro- 15 treatment the batch was maintained atalow temportion being lost through hydrolysis. The result perature, 35 C. or less, for all but about two is that a portion of the acid is not rendered hours ofthe treating time. soluble by conversion to the alginate. The ratio of oxide: to acid in these experiments was such o EFFECTS or VARIATIONINOXIDE ACID RATIO as to produce a fully satisfactory product under A soluble product, though not of the best quaimore favorable conditions, as evidenced by the ity. may be made under favoring conditions with result of the treatment at 50. At this tem'- the use of as little as one mol alkylene oxide to perature the reaction between oxide and acid is one mol of a modified acid. The eiects which folmuch accelerated and a soluble product is ob- 25 low from increase in the ratio of oxide to acid are tained. At 70 hydrolysis of the oxide is so rapid exhibited in the following table:

Table Percent Carboxyl Groups arma Pr A Lglidectii) .geutmh Ester Hom plflllg o im? ized med TW 2o as 59 7 3.2 Hazy.

2o 45 e5 22 3.a short.

2o 57 v1 '1 3.4 Bright.

2o 61 s1 22 3.5 D5.

zo so se 1 3.5 D0.

1o 75 a5 22 3.5 snm.

sa 9s 7 4.a Blight.

15 sz 97 22 13 Do.

that it is consumed before the glycol alginate reaction can complete itself, unless restrained by partial neutralization. Comparison of the results shown in the last two lines of the table illustrates this restraining eect on hydrolysis and the accompanying increase in esteriiication. At this temperature, however, an incompletely soluble product is formed, even from the modified acid,

perhaps due to a secondary reaction of the glycol alginate with ammonium salts.

The optimum temperature for esteriiication is thus very deiinitely above C. and below 70, and the indications are that it lies Within the range from to 60 C., varying somewhat with other conditions.

.Errscrs or Vanxnrc TREATING Trui:

'I'he eects of time variations are shown in the following table, reciting the Vresults obtained in treating samples of alginic acid with an alkylene oxide under conditions which were identical except as to percentage neutralization:

The term "short as used in the above table signifies that a solution of 1% weight concentration showed a very slight tendency toward gelatinization and poured in blobs, whereas the bright and hazy solutions would draw into a long string and behave as extremely viscous liquids.

The conditions obtaining in the above experiments were all favorable and the indications are that to realize complete solubility and a satisfactory degree of stability it is desirable to use not less than 1.5 mols of the alkylene oxide to one mol of a partially neutralized acid, and that to obtain substantially complete esterication of the carboxyl groups left free after partial neutralization it is desirable to increase this ratio to about 3:1. However, a result useful for many purposes is had with a molar ratio as low as 1:1 where a partially neutralized acid is used.

Acro COMPATIBILITY It was anticipated that partial neutralization, with the consequent production of a water-soluble salt of alginic acid which would pass unchanged into the glycol alginate product, would render the product incompatible with acids. This did not prove to be the case. All the products of the above described process, even such as had up to 30% of their carboxyl groups combined with a base, were completely compatible with acids, giving no precipitate and showing no tendency to gel when strongly acidied.

CALCIUM RmcnvITY No means has yet been found for preparing a glycol aginate which is completely immune to gelatinization when its concentrated aqueous solutions are mixedwith strong solutions of salts of the alkaline-earth or of the heavy metals.

concentration and at a pH value of 4.5 is mixed with a solution of calcium chloride, a hard gel is formed; at 0.6% concentration and the same pH the gel is soft; at 0.4% concentration there is a trace of gel formation, which disappears at 0.3% concentration. At pH 3.5 the concentration tolerance is materially increased, being about 0.6% to avoid any gelatinization; at pH 2.5 the concentration may be about 1.0%, and at pH 1.2 there is substantially no calcium reactivity at any concentration. These iigures refer to a grade of glycol aginate which yields an extremely viscous solution at 1% concentration. With alginates giving less viscous solutions (at any given concentration) the tolerance is increased, i. e., the solution may be stronger or the pH higher without incurring calcium reactivity.

As the lowering of pH does not produce acid gelatinization, the extent to which the pH value may be lowered and the concentration tolerance increased thereby is limited only by the nature of the medium in which the glycol alginate is used. As the lowering of pH for this purpose occurs only at the time of use, it has no effect on stability which, as said, requires a relatively high pH in the product itself if it is to be stored.

TrrrxorRoPY Amay be avoided by reducing the calcium content of the acid to not exceeding 1.5% expressed as CaO. If the acid originates in a process in which a solution of a water-soluble alginate is precipitated as the calcium salt, from which the acid is regenerated by acidification with hydrochloric acid, all that is required is a renewed slight acidiiication followed by careful waterwashing. A low calcium content or calcium-free acid may also be prepared by precipitating sodium alginate from the ltered digestion liquor by the addition of alcohol, followed by dissolving the sodium alginate in fresh water and decomposing it with hydrochloric acid. The glycol alginates prepared from these low-calcium acids show no evidences of thixotropy, even after long standing in solution.

We claim as our invention:

l. In the treatment of alginic acid to produce an alkylene glycol alginate, the steps comprising: partially neutralizing the `acidity of said acid with a base of which the alginic salt is watersoluble, and treating the resultant product with an alkylene oxide.

2. In the treatment of alginic acid to produce analkylene glycol alginate, the steps comprising: combining aminor proportion of the carboxyl groups of said acid with a base of which the alginic salt is water-soluble, and esterifying at least a portion of the uncombined carboxyl groups with an alkylene oxide.

3. In the treatment of alginic acid to produce an alkylene glycolalginate, the steps comprising; combining from iive percent to twenty percent of the carboxyl groups of said acid with a base of which the alginic salt is water-soluble, and esterii'ying at least a portion of the remaining carboxyl groups with an alkylene oxide.

4. In the treatment of alginic acid to produce an alkylene glycol alginate, the steps comprising: combining from ve percent to thirty percent of the carboxyl groups of said'acid with a base of which the alginic salt is water-soluble, and esterifying at least a portion of the remaining carboxyl groups with an alkylene oxide.

5. In the treatment of alginic acid to produce an alkylene glycol alginate: the steps of treating y said acid with a base which yields water-soluble salts with alginic acid, the quantity of said base being such as to combine with only a minor proportion of the carboxyl groups of said acid, and of treating the resultant product with an alkylene oxide under conditions favorable to esteriiicatlon.

6. In the treatment of alginic acid to produce an alkylene glycol alginate: the steps of treating said acid with a base of which the alginic salt is Water-soluble, the quantity of said base being such as to combine with from ve percent to thirty percent of the carboxyl groups of said acid, and of treating the resultant product with an alkylene oxide.

7. In the treatment of alginic acid to produce an alkylene glycol alginate: the steps of treating said acid with ammonia in quantity suilicient to combine with from five percent to thirty percent of the carboxyl groups of said acid, and of treating the resultant product with an alkylene oxide.

8. In the treatment of alginic acid to produce an alkylene glycol alginate; the steps of treating said acid with gaseous ammonia under pressure and continuing said treatment until from five percent to thirty percent of the carboxyl groups of said acid have entered into combination with said ammonia, and of treating the resultant product with an alkylene oxide.

9. In the treatment of alginic acid to produce an alkylene glycol alginate, the steps comprising: blending with said acid while in a highly hydrated and roughly comminuted ccndition a dispersion in a volatile hydrophilic solvent oi' an alkaline substance of which the alginate is watersoluble; removing any excess of liquid from the mixture; comminuting the moist acid while in suspension in a gaseous stream, thereby driving of! any remaining solvent and reducing the water content of said acid within the range 45% to 55% by weight, and treating the resultant product with an alkylene oxide.

10. In the treatment of alginic acid to produce an alkylene glycol alginate, the steps comprising: adjusting the water content of said acid within the range 45% to 55% by weight; nely subdividing said acid; neutralizing from iive percent to thirty percent of thecarboxyl groups oi said acid by combination with a base of which the alginate is water-soluble, and treating the resultant product with an alkylene oxide under conditions favorable to esterivcation.

11. In the treatment of alginic acid to produce an alkylene glycol alginate free from tendency toward thixotropy, the steps comprising: preparing an alginic acid containing not to exceed 1.5% by weight of calcium as CaO; adjusting the water content of said acid within the range 45% to 55% by weight; finely subdividing said acid;

l l neutralizing from ve percent to thirty percent of the carboxyl groups of said acid by combination with a base of which the alginate is watersolubie, and treating the resultant product with an alkylene oxide.

12. In the preparation of stable alkylene glycol alginates, the steps comprising: combining a portion of the carboxyl groups of alginic acid with a base of which the alginate is water-soluble; controlling the proportion of said base to bring the hydrogen ion concentration of the iinal product to not less than 3.5 pH; treating the partially neutralized acid with an alkylene oxide at a temperature within the range 45 to 60 cent., and continuing said treatment until not substantially more then twenty percent of the carboxyl groups of said acid remain uncombined.

13. In the preparation of stable alkylene glycol alginates, the steps comprising: combining a portion of the carboxyl groups of alginic acid with a base of which the alginate is water-soluble; controlling the proportion of said base to bring the hydrogen ion concentration of the final product to not less than pH 3.5; treating the partially neutralized acid with an alkylene oxide under superatmospheric temperature and pressure, and continuing said treatment until not substantially more than twenty percent of the carboxyl groups of said acid remain uncombined.

14. In the preparation of an alkylene ghrcol alginate, the steps comprising: subjecting moist alginic acid to a step of comminution and partial drying while in suspension in a gaseous stream; introducing ammonia into said gaseous stream to combine with a portion of the carboxyl groups of said acid; continuing the aforesaid steps until from ilve percent to thirty percent of said carboxyl groups have entered into combination with said ammonia, and treating the resultant product with an alwlene oxide under conditions favorable to esteriilcation.

15. A modified, fully water-soluble, solid glycol alginate in which from iive percent to thirty percent of the carboxyl groups of alginic acid are combined a base, in which a part not to exceed twenty percent of the carboxyl groups are unreacted, and in which the remainder of the carboxyl groups are esteriiied with an alkylene oxide,

12 said glycol alginate being further characterized by a hydrogen ion concentration in 1% aqueous solution not substantially below pH 3.5, and yielding clear, viscous colloidal aqueous solutions.

16. A modied, fully water-soluble, solid glycol alginate in which from iive percent to twenty percent of the carboxyl groups of alginic acid are combined with a base of which the aiginate is water-soluble. in which a part not to exceed twenty percent of the carboxyl groups are unreacted. and in which the remainder of the carboxyl groups are in combination with an alkylene oxide as an alkylene glycol ester, said glycol alginate being further characterized by a hydrogen ion concentration in 1 aqueous solution not substantially below pH 3.5, and yielding clear, viscous colloidal aqueous solutions.

17. The composition of claim 16 wherein the base is ammonia.

18. The composition of claim 16 wherein the base is an alkali metal.

19. The composition of claim 16 wherein the base is sodium.

20. The composition of claim 16 wherein the base is magnesium.

ARNOLD B. STEINER. WILLIAM H. McNEELY.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES 'l PATENTS NumberV Name Date 1,814,986 Walsh July 14, 1931 2,158,486 Preble May 16. 1939 2,426,125 Steiner Aug. 19, 1947 FOREIGN PATENTS Number Country Date 417,556 Great Britain Oct. 8, 1934 OTHER REFERENCES Malvezin: Chem. Zentr., 1944. vol. I, pp. 757- '758, 2 pages.

Chem. Abs., vol. 39 (1945). DP. 3258-3259, 2 

15. A MODIFIED, FULLY WATER-SOLUBLE, SOLID GLYCOL ALGINATE IN WHICH FROM FIVE PERCENT TO THIRTY PERCENT OF THE CARBOXYL GROUPS OF ALGINIC ACID ARE COMBINED WITH A BASE, IN WHICH A PART NOT TO EXCEED TWENTY PERCENT OF THE CARBOXYL GROUPS ARE UNREACTED, AND IN WHICH THE REMAINDER OF THE CARBOXYL GROUPS ARE ESTERIFIED WITH AN ALKYLENE OXIDE, SAID GLYCOL ALGINATE BEING FURTHER CHARACTERIZED BY A HYDROGENION CONCENTRATION IN 1% AQUEOUS SOLUTION NOT SUBSTANTIALLY BELOW PH 3.5, AND YIELDING CLEAR, VISCOIUS COLLOIDAL AQUEOUS SOLUTIONS. 